Heretofore, polyester resins typically were made by the reaction of a diester or a diacid with a diol. If the diacid was utilized, the polyester would have some acid groups in it. Polyesters suitable for powder resin coatings desirably contain a large number of carboxyl end groups to react with epoxide compounds to cure the polyester resin. However, other than the carboxyl end groups which are contained in the polyester upon the preparation thereof, acid end groups have been added through the capping of polymers with anhydrides having two carboxylic acid groups therein, as for example set forth in U.S. Ser. No. 223,972 filed Jan. 12, 1981 and U.S. Ser. No. 223,973, filed Jan. 12, 1981. My previously filed U.S. specification bearing Ser. No. 223,973 relates to the use of anhydride additives and to the use of aromatic acids which serve to increase the activation energy necessary to induce reaction of the copolyester resin with epoxide compounds upon heating. Due to the fast reaction rate of the anhydride with the polyester, large amounts of free acid, that is in excess of 90 percent of the acid charged, remain in the resin. In contrast, the present invention does not utilize any anhydrides before or concurrent with the acid reaction and generally has less than 20 percent of a total amount charged of free acid remaining after the reaction.
U.S. Pat. No. 4,264,751 relates to a copolyester resin having minimal carboxyl terminated ends as well as the method for making it, in which a chain branching agent is generally utilized. Hence, this patent is not pertinent to the present invention.